1. Field of the Invention
The present invention relates to an apparatus for suppressing knock induced in an internal combustion engine by detecting such knock and controlling at least one of the performance characteristics of the engine.
2. Description of the Prior Art
Generally, induction of knocking is dependent on the performance characteristics of an engine including various factors such as ignition timing, air-to-fuel ratio, temperature and humidity of suction air, temperature of combustion chamber and so forth. Out of the above factors, ignition timing and air-to-fuel ratio are controllable with relative facility and low cost, so that each of them is employable as effective means in a feedback control system for knock suppression. Particularly the ignition timing control is utilized practically in many knock suppression apparatus known heretofore. In the conventional apparatus of such type based on the technique of ignition timing control, it is customary to execute a feedback control action in such a manner that the ignition timing is delayed from a preset reference point by a fixed angle upon induction of knocking or by a proper angle in conformity with the knocking intensity and, in case no knock is existent, the angular delay is reduced with a considerably great time constant (e.g. 0.5.degree./sec) to adjust the ignition timing eventually to the knock threshold point.
Although induction of knocking is dependent on a variety of factors as mentioned above, those concerned with natural phenomena such as temperature and humidity of suction air are in a relatively long variation cycle with respect to the lapse of time like a day or a season. Therefore, generation of knocking derived from any change in such factors also has a long variation cycle. In other words, knocks induced within a short period of time in one engine running mode are substantially the same, and there exists almost no difference among them with respect to the induction frequency or the average intensity. That is, the control quantities required for suppressing the knocks induced in one running mode are substantially the same within a short period of time. Therefore, in one running mode of an engine prescribed by particular running parameters, the control quantity stored previously is usable as a value for the present stage and, since the ignition-timing correction range may be narrow with regard to generation of slight-intensity knocking during the control action, high-precision knock suppression is achievable with a remarkably rapid response by executing sequential correction control in response to a knock detection signal at each time of the generation. Moreover, for any change occurring in the aforementioned long-cycle factor, the stored control quantity may be altered slowly to carry out the desired correction.